Japanese Utility Model Public Disclosure No. Sho 60-173712 discloses a securing device, which can secure together two plates and is not limited to use with plates of a specific combined thickness.
Also, Japanese Utility Model Public Disclosure No. Sho 60-173712 discloses a securing device which is provided with a plurality of engagement ribs provided upon the external peripheral surface thereof in order to be able to secure two plates together, and again which is not limited to use with plates of a specific thickness (as shown in FIGS. 6 and 7).
This securing device, as shown in FIGS. 6 and 7, comprises an outer cylinder 1 having the outer periphery thereof provided with a plurality of engagement ribs 2. With an insertion member 4 slightly inserted within the outer cylinder 1 (as shown in FIG. 6), the securing device is inserted through mounting holes A1 and B1 respectively provided within two overlapped plates A and B, and a flange 3 of the outer cylinder 1 is brought into contact with the upper surface of the upper plate A. Then, as shown in FIG. 7, the insertion member 4 is forcibly inserted into the outer cylinder 1 until a flange portion 5 of the insertion member 4 strikes the flange portion 3 of the outer cylinder 1. Consequently, the leading end of the insertion member 4 engages the inner wall of the outer cylinder 1 and spreads the cylinder 1 radially outwardly. Thus, the engagement ribs 2 are strongly urged against the edge of the mounting hole B1 of the lower plate B. In this manner, the lower plate B is secured to the upper plate A.
Since the outer cylinder 1 is provided with a plurality of engagement ribs 2, two plates can be secured together irrespective of the thickness of the plates.
With the prior art securing device having the aforenoted structure, the insertion member 4 has to be pulled upwardly in order to remove the device from the plates within which it is secured as shown in FIG. 7. However, the removal is very difficult since the flange 3 of the outer cylinder 1 and flange 5 of the insertion member 4 are disposed in close contact with each other. Further, more if the device receives strong vibrations over a long period of time while disposed in the secured state shown in FIG. 7, it is likely that the insertion member 4 will become loosened whereby, in turn, the plates A and B will be detached or loosened.